Magnesium-based alloys have been widely used as cast parts in the aerospace and automotive industries and are mainly based on the following four systems:
Mg--Al system (i.e., AM20, AM50, AM60); PA1 Mg--Al--Zn system (i.e., AZ91D); PA1 Mg--Al--Si system (i.e., AS21, AS41); and PA1 Mg--Al--Rare Earth system (i.e., AE41, AE42).
Magnesium-based alloy cast parts can be produced by conventional casting methods which include diecasting, sand casting, permanent and semi-permanent mold casting, plaster-mold casting and investment casting.
These materials demonstrate a number of particularly advantageous properties that have prompted an increased demand for magnesium-based alloy cast parts in the automotive industry. These properties include low density, high strength-to-weight ratio, good castability, easy machineability and good damping characteristics.
AM and AZ alloys, however, are limited to low-temperature applications where they are known to lose their creep resistance at temperatures above 140.degree. C. AS and AE alloys, while developed for higher temperature applications, offer only a small improvement in creep resistance and/or are expensive.
It is therefore an object of the present invention to provide relatively low cost magnesium-based alloys with improved elevated-temperature performance.
It is a more particular object to provide relatively low cost magnesium-aluminum-strontium alloys with good creep resistance, tensile yield strength and bolt-load retention, particularly at elevated temperatures of at least 150.degree. C., and good salt-spray corrosion resistance.